Without limiting the scope of the invention, its background is described in connection with organic/inorganic complexes.
In the scientific literature, the term Maya blue refers to a “turquoise” brilliant shade of blue that is found on murals and archaeological artifacts, for example, throughout Mesoamerica. It is described in the literature as being composed of palygorskite clay and indigo, that when mixed and heated, produce the stable brilliant blue color similar to that found in Mesoamerica. The ancient Mayan Indians would paint unlucky people blue, which was associated with their rain deities, and throw them down a sacred well as human sacrifices. The pigment is known to have the ability to resist age, acid, weathering, and even modern chemical solvents.
Indigo is a dye obtained from many plants, mainly those in the genus Indigofera, which are native to the tropics. In ancient times, the dye was obtained by soaking the plant leaves in water and fermenting them in order to convert a “glycoside indican” into the blue dye indigotin. Littman synthesized indigo-attapulgite complexes and verified that his synthetic version was indistinguishable from the original pigments found in the pre-Hispanic murals and artifacts (Littman, 1980; Littman, 1982). The prepared samples had the same physical and chemical characteristics as the authentic Maya blue examined. Littman concluded that the remarkable stability of the attapulgite was due to the heat treatment the attapulgite received during the synthesis. Others have also synthesized compounds similar to that of Maya blue by a number of routes (Torres, 1988). They employed the Gettens test to determine whether the laboratory synthesis of Maya blue was indeed authentic with the same chemical resistant properties (Gettens, 1962). The test was necessary because initial attempts of simply mixing the palygorskite clay produced the color of Maya blue but the mixture did not possess the same chemical properties as the original organic/inorganic complex samples.
Since ancient times, Indigo has been used as an astringent, emetic, stimulant, and antiseptic. In Mexico, the Añil (Indigofera suffruticosa) is used for children's headaches by boiling leaves until soft, then apply the leaves like a bandage to the forehead. The Chinese would use Indigofera tinctoria L. to clean the liver, detoxify the blood, reduce inflammation, alleviate pain, and reduce fever. In South Africa, the powdered root of Indigofera was used to alleviate toothaches.
U.S. Pat. No. 7,052,541 describes color compositions comprising neutral indigo derivative pigments and dyes complexed to the surface of inorganic clays. These materials are useful as paints and coatings for artistic and industrial purposes, including use in cements, plastics, papers and polymers. Upon grinding and heating the organic and inorganic component as solid mixtures or in aqueous solutions, the resulting color compositions have unprecedented stability relative to the original starting materials. Related U.S. Ser. No. 11/351,577, filed Feb. 10, 2006, describes the use of similar starting materials in methods that rely on UV-light for preparing color compositions.